Lubricating oil composition

ABSTRACT

The object of this invention is to offer a lubricating oil composition which has superior extreme pressure properties (ability to prevent welding), which generates a small amount of sludge and which also has a high viscosity index. The invention provides a lubricating oil composition to which has been added a copolymer of specified olefins and alkyl methacrylates.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition, andspecifically relates to a lubricating oil composition which has superiorextreme pressure properties, which generates a small amount of sludgeand which also has a high viscosity index.

BACKGROUND OF THE INVENTION

Attention is being paid to the generation of electricity by wind poweras a renewable energy source. In apparatus for wind-power generation ofelectricity the slow rotation of blades is speeded up by means ofstep-up gears, so that an electricity generator can be rotated by meansof their power. But there are many gear wheels in the step-up gear boxand a gear oil is required to lubricate these wheels (Gekkan Tribology,No. 273, pages 50-51, May 2010).

In particular, the scale of the apparatus for wind-power generation ofelectricity has increased in recent years, and since it is necessary toconvert large slow forces to high speed by means of step-up gearing, theburden on the gear wheels within the gearing has increased, with theresult that there has been a demand for greater ability in the gear oilsthat lubricate them to resist welding (extreme pressure properties).However, the extreme pressure agents which are capable of resistingwelding when blended in gear oils are prone to turn into sludge throughageing and oxidation, and the sludge so produced may cause wear andwelding by biting into the wheels as foreign matter, and may also end upcausing problems by clogging filters and blocking oil pipes. Maintenancesuch as carrying out oil changes early before too large amounts ofsludge are generated in the oil is therefore important.

At the same time, apparatus for wind-power generation of electricity isoften located in remote areas such as mountainous regions or sea shores,so that frequent maintenance is difficult. Also, greater costs arerequired for maintenance in out-of-the-way areas, so that, to reduceoperating costs, there is demand to extend maintenance intervals andoil-change intervals. In order, therefore, to reduce costs forprotection and operation of the gear wheels, there has been demand toimprove the oxidative stability performance of gear oils and to minimisethe amount of sludge created.

Also, apparatus for wind-power generation of electricity is runcontinuously under a wide range of temperature conditions in response tofluctuations between day and night and weather conditions, and so therehas likewise been demand for the gear oil used to have smallfluctuations in viscosity due to temperature change, that is to have ahigh viscosity index.

Given the above, there has been demand for an industrial-levellubricating oil which has superior extreme pressure properties (abilityto prevent welding), which generates a small amount of sludge and whichalso has a high viscosity index.

The problem to be addressed by the present invention is to offer alubricating oil composition which has superior extreme pressureproperties (ability to prevent welding), which generates a small amountof sludge and which also has a high viscosity index.

SUMMARY OF THE INVENTION

By dint of various and repeated investigations and research to reducethe amount of sludge generated in an industrial-level lubricating oil,the inventors arrived at this invention after discovering that when acopolymer of a specified olefin and an alkyl methacrylate is added in agiven fixed range of molecular weights, the amount of sludge generatedis reduced, and in addition the viscosity index improves.

In general, copolymers of olefins and alkyl methacrylates are used inlubricating oil compositions as viscosity index improvers, but nothinghas been known about reducing the amount of sludge generated. Thisinvention is an attempt to reduce the amount of sludge by adding acopolymer of an olefin and an alkyl methacrylate as an effectiveconstituent to a lubricating oil base oil which contains an extremepressure agent.

Accordingly the present invention provides a lubricating oil compositioncomprising (A) 50 to 90% by mass of at least one kind of lubricating oilbase oil selected from mineral oils and synthetic oils and (B) 10 to 50%by mass of a copolymer, being of molecular weight 1200 to 50,000, of anolefin and an alkyl methacrylate.

According to this invention, a lubricating oil composition which hassuperior extreme pressure properties (ability to prevent welding), whichgenerates a small amount of sludge and which also has a high viscosityindex is obtained. By reducing the amount of sludge generated byoxidative ageing, wear and welding due to foreign matter becomingembedded are inhibited, and the service life of the machinery (forexample, gears) is extended. Also, the fact that the viscosity index ishigher means that low temperature flow characteristics are superior andan oil film can be maintained at higher temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the molecular weight distribution curves for Additive A1and Additive A2.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a lubricating oil composition characterised inthat it comprises (A) at least one kind of lubricating oil base oilselected from mineral oils and synthetic oils and (B) a copolymer of anolefin and an alkyl methacrylate of molecular weight within a specifiedrange. The lubricating oil comprises components (A) and (B), but inparticular embodiments the lubricating oil may contain components (A)and (B) or may consist essentially of components (A) and (B).

For the base oil of the present lubricating oil composition it ispossible to use the mineral oils and synthetic oils known as highlyrefined base oils, and in particular it is possible to use, singly or asmixtures, base oils which belong to Group II, Group III and Group IV ofthe API (American Petroleum Institute) base oil categories. For the baseoils used here, the sulphur content is not more than 300 ppm, butpreferably not more than 200 ppm, more preferably not more than 100 ppm,and most preferably not more than 50 ppm. Also, the density is 0.8 to0.9 g/cm³, but preferably 0.8 to 0.865 g/cm³, and more preferably 0.81to 0.83 g/cm³. The aromatic content (aromatic contents in this inventionare determined by n-d-M analysis in accordance with ASTM D3238) is lessthan 3%, but preferably less than 2% and more preferably less than 0.1%.

As examples of Group II base oils, mention may be made of paraffinicmineral oils obtained by appropriate use of a suitable combination ofrefining processes such as hydrorefining and dewaxing in respect oflubricating oil fractions obtained by atmospheric distillation of crudeoil. Group II base oils refined by hydrorefining methods such as theGulf Company method have a total sulphur content of less than 10 ppm andan aromatic content of not more than 5% and so are suitable for thisinvention. The viscosity of these base oils is not specially limited,but the viscosity index (viscosity indexes in this invention aredetermined in accordance with ASTM D2270 and JIS K2283) should be 80 to120 and preferably 100 to 120. The kinematic viscosity at 40° C.(kinematic viscosities in this invention are determined in accordancewith ASTM D445 and JIS K2283) should preferably be 2 to 680 mm²/s andeven more preferably 8 to 220 mm²/s. Also, the total sulphur contentshould be less than 300 ppm, preferably less than 200 ppm and even morepreferably less than 10 ppm. The total nitrogen content should be lessthan 10 ppm and preferably less than 1 ppm. In addition, oils with ananiline point (aniline points in this invention are determined inaccordance with ASTM D611 and JIS K2256) of 80 to 150° C. and preferably100 to 135° C. should be used.

Suitable Group III and Group II+ base oils include paraffinic mineraloils manufactured by a high degree of hydrorefining in respect oflubricating oil fractions obtained by atmospheric distillation of crudeoil, base oils refined by the Isodewaxing process which dewaxes andsubstitutes the wax produced by the dewaxing process with isoparaffins,and base oils refined by the Mobil wax isomerisation process. Theviscosity of these base oils is not specially limited, but the viscosityindex should be 95 to 145 and preferably 100 to 140. The kinematicviscosity at 40° C. should preferably be 2 to 680 mm²/s and even morepreferably 8 to 220 mm²/s. Also, the total sulphur content should be 0to 100 ppm and preferably less than 10 ppm. The total nitrogen contentshould be less than 10 ppm and preferably less than 1 ppm. In addition,oils with an aniline point of 80 to 150° C. and preferably 110 to 135°C. should be used.

GTLs (gas to liquid) synthesised by the Fischer-Tropsch method ofconverting natural gas to liquid fuel have a very low sulphur contentand aromatic content compared with mineral oil base oils refined fromcrude oil and have a very high paraffin constituent ratio, and so haveexcellent oxidative stability, and because they also have extremelysmall evaporation losses, they are suitable as base oils for thisinvention. The viscosity characteristics of GTL base oils are notspecially limited, but normally the viscosity index should be 130 to 180and preferably 140 to 175. Also, the kinematic viscosity at 40° C.should be 2 to 680 mm2/s and preferably 5 to 120 mm2/s.

Normally the total sulphur content should also be less than 10 ppm andthe total nitrogen content less than 1 ppm. A commercial example of sucha GTL base oil is Shell XHVI (registered trademark).

As examples of synthetic oils mention may be made of polyolefins,alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols,polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds(perfluoropolyethers, fluorinated polyolefins) and silicone oils, ormixtures thereof.

The aforementioned polyolefins include polymers of various olefins orhydrides thereof. Any olefin may be used, and as examples mention may bemade of ethylene, propylene, butene and α-olefins with five or morecarbons. In the manufacture of the polyolefins, one kind of theaforementioned olefins may be used singly or two or more kinds may beused in combination.

Particularly suitable are the polyolefins called polyalphaolefins (PAO).These are base oils of Group IV. The polyalphaolefins may also bemixtures of two or more kinds of synthetic oil.

The viscosity of these synthetic oils is not specially limited, but thekinematic viscosity at 40° C. should be 2 to 680 mm²/s, but preferably20 to 500 mm²/s and more preferably 30 to 450 mm²/s. The kinematicviscosity at 100° C. of said synthetic base oils should be 2 to 100mm²/s, but preferably 4 to 70 mm²/s and more preferably 6 to 50 mm²/s.The viscosity index of said synthetic base oils should be 110 to 170,but preferably 120 to 160 and more preferably 130 to 155. The 15° C.density of said synthetic base oils should be 0.8000 to 0.8600 g/cm³,but preferably 0.8100 to 0.8550 g/cm³ and more preferably 0.8250 to0.8550 g/cm³. The aniline point of said synthetic base oils should be110 to 180° C., but preferably 120 to 170° C. and more preferably 130 to165° C.

The amount of the aforementioned base oil to be incorporated in thelubricating oil composition of this invention is not specially limited,but, taking as a basis the total amount of the lubricating oilcomposition, a typical range can be given as 50 to 90 wt %, butpreferably 50 to 80 wt % and more preferably 50 to 70 wt %. The lowerlimit of the amount incorporated in the base oil, on the basis of thetotal amount of the lubricating oil composition, should be selected fromany of not less than 50, 51, 52, 53, 54, 55, 56, 57, 58 or 59 wt %, andthe upper limit of the amount incorporated in the base oil, on the basisof the total amount of the lubricating oil composition, should beselected from any of not more than 67, 68, 69 or 70 wt %.

Apart from what is stated above, said base oils may also includecarboxylic acid ester compounds. These are discussed below.

As examples of the copolymers of olefins and alkyl methacrylates of thepresent lubricating oil composition, mention may be made of copolymersin which the essential constituent monomers are at least one kind ofolefin having 2 to 20 carbons and at least one kind of alkylmethacrylate having alkyl groups with 1 to 20 carbons.

The aforementioned olefins include various kinds of olefin polymers orhydrides thereof. Any olefin may be used, but as examples mention may bemade of ethylene, propylene, butene, pentene, hexene, heptene, octene,nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene,hexadecene, heptadecene, octadecene, nonadecene and eicosene. It is alsopossible to use a single kind of the aforementioned olefins orcombinations of two or more kinds for the olefins comprised in theconstituent monomers.

As specific examples of the aforementioned alkyl methacrylates havingalkyl groups with 1 to 20 carbons, mention may be made of:

(1) alkyl methacrylates having alkyl groups with 1 to 4 carbons: forexample, methyl methacrylate, ethyl methacrylate, n- or iso-propylmethacrylate, n-, iso- or sec-butyl methacrylate;

(2) alkyl methacrylates having alkyl groups with 8 to 20 carbons: forexample, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decylmethacrylate, n-isodecyl methacrylate, n-undecyl methacrylate, n-dodecylmethacrylate, 2-methylundecyl methacrylate, n-tridecyl methacrylate,2-methyldodecyl methacrylate, n-tetradecyl methacrylate,2-methyltridecyl methacrylate, n-pentadecyl methacrylate,2-methyltetradecyl methacrylate, n-hexadecyl methacrylate, andn-octadecyl methacrylate, n-eicosyl methacrylate, n-docosylmethacrylate, methacrylate of Dobanol 23 [mixture of C-12/C-13oxoalcohols made by Mitsubishi Chemical (Ltd.)] and methacrylate ofDobanol 45 [mixture of C-13/C-14 oxoalcohols made by Mitsubishi ChemicalCompany Ltd.];

(3) alkyl methacrylates having alkyl groups with 5 to 7 carbons: forexample, n-pentyl methacrylate and n-hexyl methacrylate.

Of the aforementioned monomers (1)˜(3), the preferred ones are thosebelonging to (1) and (2), and the monomers of (2) are further preferred.Also, the preferred monomers of the aforementioned (1), from thestandpoint of the viscosity index, are those with 1 to 2 carbons in thealkyl groups. The preferred monomers of the aforementioned (2), from thestandpoint of solubility in the base oil and low-temperaturecharacteristics, are those with 10 to 20 carbons in the alkyl groups,and further preferred are those with 12 to 14 carbons.

The molecular weight of the aforementioned olefin and alkyl methacrylatecopolymers is 1,200 to 80,000, but preferably 1,200 to 50,000 and morepreferably 2,000 to 50,000. The weight average molecular weight is 5,000to 30,000, but preferably 7,000 to 20,000 and more preferably 9,000 to16,000. The number average molecular weight is 2,000 to 12,000, butpreferably 4,000 to 10,000 and more preferably 5,000 to 9,000. In thecase of these molecular weights, the weight average molecular weight(Mw) and number average molecular weight (Mn) are those determined bymeans of gel permeation chromatography (GPC), and are those obtained byconversion, taking polystyrene as the standard.

The aforementioned weight average molecular weight can be regulated bymeans of the temperature during polymerisation, the monomerconcentration (solvent concentration), the amount of catalyst or theamount of chain transfer agent.

The dispersion (Mw/Mn) of the aforementioned olefin and alkylmethacrylate copolymers is 1 to 2.5, but preferably 1.3 to 2.2 andespecially 1.7 to 1.9.

The viscosity of the aforementioned olefin and alkyl methacrylatecopolymers is not specially limited, but the viscosity index should be100 to 250, but preferably 130 to 220 and more preferably 160 to 200.The kinematic viscosity at 40° C. of said copolymers should be 1,000 to12,000 mm²/s, but preferably 2,000 to 10,000 mm²/s and more preferably2,500 to 9,000 mm²/s. The kinematic viscosity at 100° C. of saidcopolymers should be 50 to 600 mm²/s, but preferably 100 to 500 mm²/sand more preferably 150 to 450 mm²/s. The 15° C. density of saidcopolymers should be 0.900 to 0.950 g/cm³, but preferably 0.910 to 0.940g/cm³ and more preferably 0.925 to 0.935 g/cm³.

The copolymers of this invention can be readily obtained by any of theusual methods, and the method of manufacture is not limited. Forexample, they can be obtained by radical polymerisation using a diluent,olefins and alkyl methacrylates of selected kinds and amounts, acopolymerisation initiator and a chain transfer agent. They can also beobtained by thermal polymerisation of olefins and alkyl methacrylates ofselected kinds and amounts with a diluent. The use of a diluent isoptional, but the use of a diluent makes it easier to control themolecular weight of the copolymer. It is also thus often possible toresolve problems to do with handling, because copolymers have viscousproperties. Any diluent may be used so long as it an inert hydrocarbon,but it must have solubility properties for the copolymer and lubricatingoil. As examples of suitable copolymerisation initiators, mention may bemade of initiators which break down through application of heat andproduce free radicals, for instance peroxide compounds such as benzoylperoxide, t-butyl peroctoate and cumene hydroperoxide, and azo compoundssuch as azobisisobutyronitrile and 2,2′-azobis(2-methylbutanenitrile).As examples of suitable chain transfer agents mention may be made ofthose normally used in the art, for instance α-styrene dimers,dodecylmercaptan and ethylmercaptan. The use of a chain transfer agentis optional, but the use of a chain transfer agent makes it easier tocontrol the molecular weight of the copolymer.

The amount of the aforementioned olefin and alkyl methacrylate copolymerin the lubricating oil composition of this invention (the amount of theaforementioned olefin and alkyl methacrylate copolymer within theaforementioned molecular weight range) is not specially limited, but,taking as a basis the total amount of the lubricating oil composition, atypical range can be given as 10 to 50 wt %, but preferably 10 to 45 wt% and more preferably 15 to 40 wt %. The lower limit of the amount ofolefin and alkyl methacrylate copolymer, on the basis of the totalamount of the lubricating oil composition, should be selected from anyof not less than 10, 11, 12, 13, 14 or 15 wt %, and the upper limit ofthe amount incorporated in the base oil, on the basis of the totalamount of the lubricating oil composition, should be selected from anyof not more than 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 wt %. Themethod of determining the amount of said copolymer within a certainmolecular weight range in this case is not specially limited, and can bea value converted theoretically from molecular weight distributioncurves. For example, when using additives containing said copolymers asraw material {containing olefin and alkyl methacrylate copolymers withinthe aforementioned specified range (a suitable range or especiallysuitable range appertaining thereto), olefin and alkyl methacrylatecopolymers divergent from said specified range and diluents}, molecularweight distribution curves may be produced by analysing said additives(see, for example, FIG. 1). The molecular weight component of aspecified range (say, 1200 to 50000) in said molecular weightdistribution curves is inferred to be an “olefin and alkyl methacrylatecopolymer within said specified range” and the amount of the componentwithin said specified range in the total additive is calculated on thebasis of said molecular weight distribution curves.

In the case of the present lubricating oil composition, theaforementioned lubricating oil base oil may contain carboxylic acidester compounds.

As examples of carboxylic acid ester compounds, mention may be made ofpolyol esters. As examples of polyol esters mention may be made oftrihydroxymethylpropyl trioleate (CAS No. 11138-60-6), esters of TMP(trimethylolpropane) and carboxylic acids, esters of PE(pentaerythritol) and carboxylic acids, dicarboxylic acid esters andtrimellitic acid esters. The number of carbons in the carboxylic acidresidual groups of the ester molecules should also preferably be from 4to 20 but more preferably from 6 to 18.

The amount of the aforementioned carboxylic acid ester incorporated inthe lubricating oil composition of this invention is not speciallylimited, but, taking as a basis the total amount of the lubricating oilcomposition, a typical range can be given as 5 to 15 wt %, butpreferably 7 to 13 wt % and more preferably 8 to 12 wt %. The amount ofcarboxylic acid ester incorporated, on the basis of the total amount ofthe lubricating oil composition, should be selected from any of 5, 6, 7,8, 9, 10, 11, 12, 13, 14 or 15 wt %.

In order to improve performance further, it is possible where necessaryto make appropriate use of various kinds of additives other than theaforementioned constituents. As examples of these, mention may be madeof anti-oxidants, metal deactivators, extreme pressure agents, oilinessimprovers, defoaming agents, viscosity index improvers, pour-pointdepressants, detergent-dispersants, rust preventatives, demulsifyingagents, and other lubricating oil additives of the known art.

For the anti-oxidants used in this invention, those used in lubricatingoils are preferred for practical use, and mention may be made ofamine-based anti-oxidants, sulphur-based anti-oxidants, phenol-basedanti-oxidants and phosphorus-based anti-oxidants. These anti-oxidantsmay be used singly or in plural combinations within the range of 0.01 to5 parts by weight relative to 100 parts by weight of the base oil.

As examples of the aforementioned amine-based anti-oxidants, mention maybe made of dialkyl-diphenylamines such as p,p′-dioctyl-diphenylamine(Nonflex OD-3, made by Seiko Chemical Ltd),p,p′-di-α-methylbenzyl-diphenylamine andN-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such asmono-t-butyldiphenylamine and monooctyldiphenylamine,bis(dialkylphenyl)amines such as di(2,4-diethylphenyl)amine anddi(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such asoctyl-phenyl-1-naphthylamine and N-t-dodecylphenyl-1-naphthylamine,1-naphthylamine, aryl-naphthylamines such as phenyl-1-naphthylamine,phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine andN-octylphenyl-2-naphthylamine, phenylenediamines such asN,N′-diisopropyl-p-phenylenediamine andN,N′-diphenyl-p-phenylenediamine, and phenothiazines such asPhenothiazine (made by Hodogaya Chemical Ltd.) and3,7-dioctylphenothiazine.

As examples of sulphur-based anti-oxidants, mention may be made ofdialkyl sulphides such as didodecyl sulphide and dioctadecyl sulphide,thiodipropionate esters such as didodecyl thiodipropionate, dioctadecylthiodipropionate, dimyristyl thiodipropionate and dodecyloctadecylthiodipropionate, and 2-mercaptobenzoimidazole.

Phenol-based anti-oxidants include 2-t-butylphenol,2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol,2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol,2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol,2,5-di-t-butylhydroquinone (Antage DBH, made by Kawaguchi ChemicalIndustry Co. Ltd.), 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-alkylphenolssuch as 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol,and 2,6-di-t-butyl-4-alkoxyphenols such as2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol.

Also, there are 3,5-di-t-butyl-4-hydroxybenzylmercapto-octylacetate,alklyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such asn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (Yoshinox SS,made by Yoshitomi Fine Chemicals Ltd.),n-dodecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, andbenzenepropanoic acid 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-C7˜C9side-chain alkyl esters (Irganox L135, made by Ciba Specialty ChemicalsLtd.), 2,6-di-t-butyl-α-dimethylamino-p-cresol, and2,2′-methylenebis(4-alkyl-6-t-butylphenol)s such as2,2′-methylenebis(4-methyl-6-t-butylphenol) (Antage W-400, made byKawaguchi Chemical Industry Ltd.) and2,2′-methylenebis(4-ethyl-6-t-butylphenol) (Antage W-500, made byKawaguchi Chemical Industry Ltd).

Furthermore, there are bisphenols such as4,4′-butylidenebis(3-methyl-6-t-butylphenol) (Antage W-300, made byKawaguchi Chemical Industry Ltd.),4,4′-methylenebis(2,6-di-t-butylphenol) (Ionox 220AH, made by ShellJapan Ltd.), 4,4′-bis(2,6-di-t-butylphenol),2,2-(di-p-hydroxyphenyl)propane (Bisphenol A, made by Shell Japan Ltd.),2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane,4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethylene glycolbis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (Irganox L109, made byCiba Specialty Chemicals Ltd.), triethylene glycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] (Tominox 917, madeby Yoshitomi Fine Chemicals Ltd.),2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (IrganoxL115, made by Ciba Specialty Chemicals Ltd.),3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane(Sumilizer GA80, made by Sumitomo Chemicals),4,4′-thiobis(3-methyl-6-t-butylphenol) (Antage RC, made by KawaguchiChemical Industry Ltd.) and 2,2′-thiobis(4,6-di-t-butyl-resorcinol).

Mention may also be made of polyphenols such astetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]methane(Irganox L101, made by Ciba Specialty Chemicals Ltd.),1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Yoshinox 930, madeby Yoshitomi Fine Chemicals Ltd.),1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (Ionox330, made by Shell Japan Ltd.),bis-[3,3′-bis-(4′-hydroxy-3′-t-butylphenyl) butyric acid]glycol ester,2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenoland 2,6,-bis(2′-hydroxy-3′-t-butyl-5′-methyl-benzyl)-4-methylphenol, andphenol-aldehyde condensates such as condensates of p-t-butylphenol andformaldehyde and condensates of p-t-butylphenol and acetaldehyde.

As examples of phosphorus-based anti-oxidants mention may be made oftriarylphosphites such as triphenylphosphite and tricresylphosphite,trialkylphosphites such as trioctadecylphosphite and tridecylphosphite,and tridodecyltrithiophosphite.

Metal deactivators that can be used together with the composition ofthis invention include benzotriazole and benzotriazole derivatives whichare 4-alkyl-benzotriazoles such as 4-methyl-benzotriazole and4-ethyl-benzotriazole, 5-alkyl-benzotriazoles such as5-methyl-benzotriazole and 5-ethyl-benzotriazole, 1-alkyl-benzotriazolessuch as 1-dioctylaminomethyl-2,3-benzotriazole and 1-alkyl-tolutriazolessuch as 1-dioctylaminomethyl-2,3-tolutriazole, and benzoimidazole andbenzoimidazole derivatives which are 2-(alkyldithio)-benzoimidazolessuch as 2-(octyldithio)-benzoimidazole, 2-(decyldithio)-benzoimidazoleand 2-(dodecyldithio)-benzoimidazole and 2-(alkyldithio)toluimidazolessuch as 2-(octyldithio)-toluimidazole, 2-(decyldithio)-toluimidazole and2-(dodecyldithio)toluimidazole.

Also, mention may be made of indazole, indazole derivatives which aretoluindazoles such as 4-alkyl-indazoles and 5-alkyl-indazoles,benzothiazole, and benzothiazole derivatives which are2-mercaptobenzothiazole derivatives (Thiolite B-3100, made by ChiyodaChemical Industries Ltd.), 2-(alkyldithio)benzothiazoles such as2-(hexyldithio)benzothiazole and 2-(octyldithio)benzothiazole,2-(alkyldithio)toluthiazoles such as 2-(hexyldithio)toluthiazole and2-(octyldithio)toluthiazole,2-(N,N-dialkylydithiocarbamyl)-benzothiazoles such as2-(N,N-diethyldithiocarbamyl)-benzothiazole,2-(N,N-dibutyldithiocarbamyl)-benzothiazole and2-(N,N-dihexyldithiocarbamyl)-benzothiazole, and2-(N,N-dialkylydithiocarbamyl)-benzothiazoles such as2-(N,N-diethyldithiocarbamyl)-toluthiazole,2-(N,N-dibutyldithiocarbamyl)-toluthiazole and2-(N,N-dihexyldithiocarbamyl)-toluthiazole.

Further, mention may be made of benzooxazole derivatives which are2-(alkyldithio)benzooxazoles such as 2-(octyldithio)benzooxazole,2-(decyldithio)benzooxazole and 2-(dodecyldithio)benzooxazole or whichare 2-(alkyldithio)toluoxazoles such as 2-(octyldithio)toluoxazole,2-(decyldithio)toluoxazole and 2-(dodecyldithio)toluoxazole, thiadiazolederivatives which are 2,5-bis(alkyldithio)-1,3,4-thiadiazoles such as2,5-bis(heptyldithio)-1,3,4-thiadiazole,2,5-bis(nonyldithio)-1,3,4-thiadiazole,2,5-bis(dodecyldithio)-1,3,4-thiadiazole and2,5-bis(octadecyldithio)-1,3,4-thiadiazole,2,5-bis(N,N-dialkyldithiocarbamyl)-1,3,4-thiadiazoles such as2,5-bis(N,N-diethyldithiocarbamyl)-1,3,4-thiadiazole,2,5-bis(N,N-dibutyldithiocarbamyl)-1,3,4-thiadiazole and2,5-bis(N,N-dioctyldithiocarbamyl)-1,3,4-thiadiazole and2-N,N-dialkyldithiocarbamyl-5-mercapto-1,3,4-thiadiazoles such as2-N,N-dibutyldithiocarbamyl-5-mercapto-1,3,4-thiadiazole and2-N,N-dioctyldithiocarbamyl-5-mercapto-1,3,4-thiadiazole, and triazolederivates which are, for example, 1-alkyl-2,4-triazoles such as1-di-octylaminomethyl-2,4-triazole. These metal deactivators may be usedsingly or in plural combinations within the range of 0.01 to 0.5 part byweight relative to 100 parts by weight of the base oil.

It is possible also to add phosphorus compounds to the lubricating oilcomposition of this invention in order to impart anti-wear propertiesand extreme-pressure properties. As examples of phosphorus compoundssuitable for this invention, mention may be made of phosphate esters,acidic phosphate esters, amine salts of acidic phosphate esters, basicphosphate esters, phosphite esters, phosphorothionates, zincdithiophosphates, esters of dithiophosphoric acid and alkanols orpolyether-type alcohols, and derivatives thereof, phosphorus-containingcarboxylic acids and phosphorus-containing carboxylic acid esters. Thesephosphorus compounds may be used singly or in plural combinations withinthe range of 0.01 to 2 parts by weight relative to 100 parts by weightof the base oil.

As examples of the aforementioned phosphate esters, mention may be madeof tributyl phosphate, tripentyl phosphate, trihexyl phosphate,triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecylphosphate, triundecyl phosphate, tridodecyl phosphate, tritridecylphosphate, tritetradecyl phosphate, tripentadecyl phosphate,trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate,trioleyl phosphate, triphenyl phosphate,tris(iso-propylphenyl)phosphate, triallyl phosphate, tricresylphosphate, trixylenyl phosphate, cresyldiphenyl phosphate andxylenyldiphenyl phosphate.

As specific examples of the aforementioned acidic phosphate esters,mention may be made of monobutyl acid phosphate, monopentyl acidphosphate, monohexyl acid phosphate, monoheptyl acid phosphate,monooctyl acid phosphate, monononyl acid phosphate, monodecyl acidphosphate, monoundecyl acid phosphate, monododecyl acid phosphate,monotridecyl acid phosphate, monotetradecyl acid phosphate,monopentadecyl acid phosphate, monohexadecyl acid phosphate,monoheptadecyl acid phosphate, monooctadecyl acid phosphate, monooleylacid phosphate, dibutyl acid phosphate, dipentyl acid phosphate, dihexylacid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonylacid phosphate, didecyl acid phosphate, diundecyl acid phosphate,didodecyl acid phosphate, ditridecyl acid phosphate, ditetradecyl acidphosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate,diheptadecyl acid phosphate, dioctadecyl acid phosphate and dioleyl acidphosphate.

As examples of the aforementioned amine salts of acidic phosphateesters, mention may be made of the methylamine, ethylamine, propylamine,butylamine, pentylamine, hexylamine, heptylamine, octylamine,dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, trimethylamine,triethylamine, tripropylamine, tributylamine, tripentylamine,trihexylamine, triheptylamine and trioctylamine salts of the previouslymentioned acidic phosphate esters.

As examples of the aforementioned phosphite esters, mention may be madeof dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptylphosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite,diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenylphosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite,trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonylphosphite, tridecyl phosphite, triundecyl phosphite, tridodecylphosphite, trioleyl phosphite, triphenyl phosphite and tricresylphosphite.

As examples of the aforementioned phosphorothionates, mention may bemade specifically of tributyl phosphorothionate, tripentylphosphorothionate, trihexyl phosphorothionate, triheptylphosphorothionate, trioctyl phosphorothionate, trinonylphosphorothionate, tridecyl phosphorothionate, triundecylphosphorothionate, tridodecyl phosphorothionate, tritridecylphosphorothionate, tritetradecyl phosphorothionate, tripentadecylphosphorothionate, trihexadecyl phosphorothionate, triheptadecylphosphorothionate, trioctadecyl phosphorothionate, trioleylphosphorothionate, triphenyl phosphorothionate, tricresylphosphorothionate, trixylenyl phosphorothionate, cresyldiphenylphosphorothionate, xylenyldiphenyl phosphorothionate,tris(n-propylphenyl) phosphorothionate, tris(isopropylphenyl)phosphorothionate, tris(n-butylphenyl) phosphorothionate,tris(isobutylphenyl) phosphorothionate, tris(s-butylphenyl)phosphorothionate and tris(t-butylphenyl) phosphorothionate. Mixtures ofthese may also be used.

As examples of the aforementioned zinc dithiophosphates, mention may bemade in general of zinc dialkyl dithiophosphates, zinc diaryldithiophosphates and zinc arylalkyl dithiophosphates. For example, zincdialkyl dithiophosphates where the alkyl groups of the zinc dialkyldithiophosphates have primary or secondary alkyl groups of 3˜22 carbonsor alkylaryl groups substituted with alkyl groups of 3˜18 carbons may beused. As specific examples of zinc dialkyl dithiophosphates, mention maybe made of zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate,zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zincdiisopentyl dithiophosphate, zinc diethylhexyl dithiophosphate, zincdioctyl dithiophosphate, zinc dinonyl dithiophosphate, zinc didecyldithiophosphate, zinc didodecyl dithiophosphate, zinc dipropylphenyldithiophosphate, zinc dipentylphenyl dithiophosphate, zincdipropylmethylphenyl dithiophosphate, zinc dinonylphenyldithiophosphate, zinc didodecylphenyl dithiophosphate and zincdidodecylphenyl dithiophosphate.

It is possible to incorporate fatty acid esters of polyhydric alcoholsin the lubricating oil composition of this invention with a view toimproving oiliness. For example, it is possible to use partial orcomplete esters of saturated or unsaturated fatty acids having 1˜24carbons of polyhydric alcohols such as glycerol, sorbitol, alkyleneglycol, neopentyl glycol, trimethylolpropane, pentaerythritol andxylidol, and further it is also possible to incorporate those made withkinds different from the aforementioned carboxylic acid ester compounds.

Examples of glycerol esters include glycerol monolaurylate, glycerolmonostearate, glycerol monopalmitate, glycerol monooleate, glyceroldilaurylate, glycerol distearate, glycerol dipalmitate and glyceroldioleate. For sorbitol esters mention may be made of sorbitolmonolaurylate, sorbitol monopalmitate, sorbitol monostearate, sorbitolmonooleate, sorbitol dilaurylate, sorbitol dipalmitate, sorbitoldistearate, sorbitol dioleate, sorbitol tristearate, sorbitoltrilaurylate, sorbitol trioleate, and sorbitol tetraoleate.

Alkylene glycol esters include ethylene glycol monolaurylate, ethyleneglycol monostearate, ethylene glycol monooleate, ethylene glycoldilaurylate, ethylene glycol distearate, ethylene glycol dioleate,propylene glycol monolaurylate, propylene glycol monostearate, propyleneglycol monooleate, propylene glycol dilaurylate, propylene glycoldistearate and propylene glycol dioleate. For neopentyl glycol estersmention may be made of neopentyl glycol monolaurylate, neopentyl glycolmonostearate, neopentyl glycol monooleate, neopentyl glycol dilaurylate,neopentyl glycol distearate and neopentyl glycol dioleate.

Trimethylolpropane esters include trimethylolpropane monolaurylate,trimethylolpropane monostearate, trimethylolpropane monooleate,trimethylolpropane dilaurylate, trimethylolpropane distearate, andtrimethylolpropane dioleate. Pentaerythritol esters includepentaerythritol monostearate, pentaerythritol monooleate,pentaerythritol dilaurylate, pentaerythritol distearate, pentaerythritoldioleate and dipentaerythritol monooleate. For such fatty acid esters ofpolyhydric alcohols it is preferable to use partial esters of polyhydricalcohols and unsaturated fatty acids.

In order to improve the low-temperature flow characteristics andviscosity characteristics, pour-point depressants and viscosity-indeximprovers may also be added to the lubricating oil composition of thisinvention. As examples of viscosity-index improvers mention may be madeof non-dispersant type viscosity-index improvers such aspolymethacrylates and olefin polymers such as ethylene-propylenecopolymers, styrene-diene copolymers, polyisobutylene and polystyrene,and dispersant type viscosity-index improvers where nitrogen-containingmonomers have been copolymerised with these, and they may be made withkinds different from the aforementioned copolymers of olefins and alkylmethacrylates. As regards the amount to be added, they may be usedwithin the range of 0.05˜20 parts by weight relative to 100 parts byweight of the base oil.

As examples of pour-point depressants mention may be made ofpolymethacrylate-based polymers. As regards the amount to be added, theymay be used within the range of approximately 0.01˜5 parts by weightrelative to 100 parts by weight of the base oil.

Defoaming agents may also be added in order to impart defoamingcharacteristics to the lubricating oil composition of this invention. Asexamples of such defoaming agents suitable for this invention, mentionmay be made of organosilicates such as dimethylpolysiloxane,diethylsilicate and fluorosilicone, and non-silicone type defoamingagents such as polyalkylacrylates. As regards the amount to be added,they may be used singly or in plural combinations within the range of0.0001 to 0.1 part by weight relative to 100 parts by weight of the baseoil.

As examples of demulsifiers suitable for this invention, mention may bemade of those in the known art normally used as additives forlubricating oils. As regards the amount to be added, they may be usedwithin the range of 0.0005 to 0.5 part by weight relative to 100 partsby weight of the base oil.

The viscosity of the lubricating oil composition of this invention isnot specially limited, but the viscosity index should be not less than130, preferably not less than 140 and more preferably not less than 150.The kinematic viscosity at 40° C. of said lubricating oil compositionshould be 140 to 320 mm²/s, but preferably 140 to 200 mm²/s and morepreferably 140 to 160 mm²/s. The amount of sludge in a Dry TOST test ofsaid lubricating oil composition should be not more than 1500 mg/kg, butpreferably not more than 1300 mg/kg and more preferably not more than1200 mg/kg. The RPVOT remainder rate in RPVOT tests on a fresh oil ofsaid lubricating oil composition and the test oil after a Dry TOST testshould be not less than 40% but preferably not less than 50% and morepreferably not less than 60%.

The lubricating oil composition of this invention is used as a machineoil, a hydraulic oil, a turbine oil, a compressor oil, a gear-tooth oil,an oil for sliding surfaces, a bearing oil or a calibration oil. Thelubricating oil composition of this invention is ideally used as a longdrain gear oil. What is meant by “long drain gear oil” in this inventionis an industrial-level gear oil with long intervals between changes ofthe lubricating oil. The intervals between lubricating oil changes arenot specially limited, but typical examples would be not less than oneyear and preferably not less than 2 years or more preferably not lessthan 3 years. In particular the lubricating oil composition of thisinvention is ideally used for the wheels of step-up gearing in apparatusfor wind-power generation of electricity.

Examples

A more specific explanation of the lubricating oil composition of thisinvention which has superior extreme pressure properties (ability toprevent welding), which generates a small amount of sludge and whichalso has a high viscosity index is given below by using examples ofembodiment and comparative examples, but the invention is not in any waylimited by these.

The following constituent materials were used for the preparation of theexamples of embodiment and comparative examples.

1. Base Oils

Polyalphaolefin (PAO) synthetic oils classified as Group IV according tothe API (American Petroleum Institute) base oil categories.

(1-1) Base oil 1: Polyalphaolefin (ordinary name: PA06, characteristicsbeing kinematic viscosity at 40° C.: 35.4 mm²/s; kinematic viscosity at100° C.: 6.44 mm²/s; viscosity index 136; 15° C. density: 0.8291 g/cm³;aniline point: 130° C.)

(1-2) Base oil 2: Polyalphaolefin (ordinary name: PA040, characteristicsbeing kinematic viscosity at 40° C.: 401 mm²/s; kinematic viscosity at100° C.: 40.3 mm²/s; viscosity index 151; 15° C. density: 0.8491 g/cm³;aniline point: 161° C.)

2. Additives

(2-1) Additive A1: Copolymer of olefin and alkyl methacrylate (ordinaryname: Viscobase 11-570, made by Evonik Ltd.)

Molecular weight: 1200 to 25,000 (FIG. 1)

Number average molecular weight: 5400

Weight average molecular weight: 9400

Molecular weight distribution: 1.7

Kinematic viscosity at 40° C.: 2,500 mm²/s

Kinematic viscosity at 100° C.: 150 mm²/s

Viscosity index: 160

15° C. Density: 0.926 g/cm³

(2-2) Additive A2: Copolymer of olefin and alkyl methacrylate (ordinaryname: Viscobase 11-574, made by Evonik Ltd.)

Molecular weight: 1200 to 50,000 (FIG. 1)

Number average molecular weight: 8000

Weight average molecular weight: 15000

Molecular weight distribution: 1.9

Kinematic viscosity at 40° C.: 9,000 mm²/s

Kinematic viscosity at 100° C.: 450 mm²/s

Viscosity index: 200

15° C. Density: 0.934 g/cm³

(2-3) Additive A3: Olefin copolymer (ordinary name: Lucant HC-1100, madeby Mitsui Chemicals Ltd.)

Number average molecular weight: 6,000

Kinematic viscosity at 40° C.: 18,900 mm²/s

Kinematic viscosity at 100° C.: 1,100 mm²/s

Viscosity index: 270

15° C. Density: 0.850 g/cm³

(2-4) Additive A4: Polyisoolefin (ordinary name: Nisseki PolybuteneHV300, made by JX Nippon Oil & Energy Corp.)

Number average molecular weight: 1,400

Kinematic viscosity at 40° C.: 26,000 mm²/s

Kinematic viscosity at 100° C.: 590 mm²/s

Viscosity index: 155

15° C. Density: 0.898 g/cm³

(2-5) Additive B: Gear-oil additives package (ordinary name: Anglamo199, made by Lubrizol Corp.)

Kinematic viscosity at 40° C.: 68 mm²/s

Kinematic viscosity at 100° C.: 8.2 mm²/s

15° C. Density: 1.07 g/cm³

Sulphur content: 29.8 to 33.8 wt %

Phosphorus content: 1.55 to 1.89 wt %

Nitrogen content: 0.85 to 1.03 wt %

Additive B: Anglamo is a known gear-oil additives package and it isstated in the Lubrizol catalogue that if 3.25 to 3.9% of this package isblended into the lubricating oil, it will satisfy the API GL-4 standard.The API GL-4 standard is divided into six categories, and the proportionof additives is larger as the number increases, thus increasing theextreme pressure properties. In the examples of embodiment, the amountof this Additive B in the formulation was made 2.0% to meet the API GL-3standard (having extreme pressure properties of at least a mediumlevel), but the amount of Additive B in the formulation is not speciallylimited.

(2-6) Additive C: Trihydroxymethylpropyl trioleate (ordinary name:Unister H327R, made by NOF Corp.)

The lubricating oil compositions of Examples of Embodiment 1 to 4 andComparative Examples 1 to 4 were prepared using the aforementionedconstituent materials and using the compositions shown in the Tables.

Dry TOST and RPVOT tests as shown below were carried out on thelubricating oil compositions of Examples of Embodiment 1 to 4 andComparative Examples 1 to 4 to observe their performance.

Dry TOST

Following the test method for the oxidative stability of turbine oils inJIS K2514, 360 ml of test oil was poured into a container and, withoutadding any water or catalyst, it was heated for 336 hours by blowing in3 litres of oxygen every hour in a 120° C. constant-temperature tank. 24hours after completion of the test, the test oil was filtered by meansof a membrane filter of 1 μm pore diameter, and the amount of sludgeproduced was measured.

RPVOT

In accordance with the test method for the rotating bomb oxidativestability test in JIS K2514, 50 g of test oil was drawn off into acontainer, and in the co-presence of 5 ml of distilled water and acopper catalyst it was placed in a bomb pressurised with oxygen at 6.3kgf/cm² at a room temperature of 25° C. The bomb was rotated 100 times aminute inside a 150° C. constant-temperature tank. The pressure insidethe bomb was recorded, and the time from the maximum pressure reachedafter introducing the bomb into the constant-temperature tank until apressure drop of 1.75 kgf/cm² was observed was measured, and this valuewas taken as the RPVOT value. The RPVOT was carried out on fresh oil andon test oil (before filtering) after completion of the TOST.

As shown in Table 1 below, Examples of Embodiment 1 and 2 in which anolefin and alkyl methacrylate copolymer has been used as a viscosityindex improver exhibit a high viscosity index of more than 150, and theamount of sludge after the Dry TOST test is less than 1,100 mg/kg. Incontrast, Comparative Example 1, which uses an olefin copolymer, has ahigh viscosity index but a large amount of sludge. Comparative Example2, which uses polyisobutylene, has little sludge but a low value for theviscosity index.

Table 2 shows the results when trihydroxymethylpropyl trioleate(Additive C) was added to Examples of Embodiment 1 and 2 and ComparativeExamples 1 and 2. Example of Embodiment 3 and Example of Embodiment 4,which used an olefin and alkyl methacrylate copolymer as a viscosityindex improver showed greater improvement of viscosity index and greaterreduction in the amount of sludge than Example of Embodiment 1 orExample of Embodiment 2 through the addition of thetrihydroxymethylpropyl trioleate. This effect due to the addition of thetrihydroxymethylpropyl trioleate is also clear from the difference inthe results between Comparative Example 3 and Comparative Example 1, andComparative Example 4 and Comparative Example 2, but compared toExamples of Embodiment 3 and 4, Comparative Example 3 still has agreater amount of sludge, and Comparative Example 4 can be seen to havea lower viscosity index.

For the RPVOT remainder rate, a value of not less than 40% ispreferable, but a value of not less than 50% is more preferable.

TABLE 1 Example of Example of Comparative Comparative Embodiment 1Embodiment 2 Example 1 Example 2 Composition Base oil 1, wt % 44.7948.79 56.58 50.46 Base oil 2, wt % 33.21 33.21 33.21 33.21 Additive A1,wt % 20.0 Additive A2, wt % 16.0 Additive A3, wt % 8.21 Additive A4, wt% 14.33 Additive B, wt % 2.0 2.0 2.0 2.0 Test Kinematic viscosity 149154 150 149 results 40° C., mm²/s Kinematic viscosity 19.6 20.7 20.318.4 100° C., mm²/s Viscosity index 151 157 157 138 Amount of sludge,mg/kg 1,065 796 1,640 574

TABLE 2 Example of Example of Comparative Comparative Embodiment 3Embodiment 4 Example 3 Example 4 Composition Base oil 1, wt % 34.7938.79 46.58 40.46 Base oil 2, wt % 33.21 33.21 33.21 33.21 Additive A1,wt % 20.0 Additive A2, wt % 16.0 Additive A3, wt % 8.21 Additive A4, wt% 14.33 Additive B, wt % 2.0 2.0 2.0 2.0 Additive C, wt % 10.0 10.0 10.010.0 Test Kinematic viscosity 140 148 139 137 results 40° C., mm²/sKinematic viscosity 18.9 20.3 19.4 17.5 100° C., mm²/s Viscosity index154 160 159 140 Amount of sludge, mg/kg 837 796 1,500 502 RPVOT value offresh oil, min 200 220 220 230 RPVOT value after test, min 130 140 110140 RPVOT remainder rate, % 65 64 50 61

1. A lubricating oil composition comprising: (A) 50 to 90% by mass of abase oil selected from the group consisting of a Group II base oil, aGroup III base oil, a Group IV base oil, and any combination thereof;(B) 10 to 50% by mass of a copolymer of an olefin having from 2 to 20carbons and an alkyl methacrylate having alkyl groups with from 1 to 20carbons, wherein the copolymer has a molecular weight of from 1,200 to50,000; and (C) 5 to 15% by mass of a carboxylic acid ester compound. 2.The lubricating oil composition according to claim 1, wherein the baseoil is a polyalphaolefin or a GTL (gas-to-liquid) oil.
 3. Thelubricating oil composition according to claim 1, wherein the copolymerhas a weight average molecular weight of from 7,000 to 20,000.
 4. Thelubricating oil composition according to claim 1, wherein the carboxylicacid ester compound is a polyol ester.
 5. The lubricating oilcomposition according to claim 1, wherein the lubricating oilcomposition has a kinematic viscosity at 40° C. of from 140 to 320mm²/s, a viscosity index of not less than 150, and produces no more than1,200 mg/kg of sludge in a Dry TOST test.
 6. (canceled)
 7. (canceled) 8.A method of lubrication comprising: supplying a lubricating oilcomposition to a surface in relative movement to another surface,wherein the lubricating oil composition comprises: (A) 50 to 90% by massof a base oil selected from the group consisting of a Group II base oil,a Group III base oil, a Group IV base oil, and any combination thereof;(B) 10 to 50% by mass of a copolymer of an olefin having from 2 to 20carbons and an alkyl methacrylate having alkyl groups with from 1 to 20carbons, wherein the copolymer has a molecular weight of from 1,200 to50,000; and (C) 5 to 15% by mass of a carboxylic acid ester compound. 9.The method according to claim 8, wherein the base oil is apolyalphaolefin or a GTL (gas-to-liquid) oil.
 10. The method accordingto claim 8, wherein the copolymer has a weight average molecular weightof from 7,000 to 20,000.
 11. The method according to claim 8, whereinthe carboxylic acid ester compound is a polyol ester.
 12. The methodaccording to claim 8, wherein the lubricating oil composition has akinematic viscosity at 40° C. of from 140 to 320 mm²/s, a viscosityindex of not less than 150, and produces no more than 1,200 mg/kg ofsludge in a Dry TOST test.
 13. The method according to claim 8, whereinthe surface is a gear.
 14. The method according to claim 13, wherein thegear is in an apparatus for wind-power generation of electricity.
 15. Amethod of lubrication comprising: supplying a lubricating oilcomposition to a surface of a gear, wherein the lubricating oilcomposition comprises: (A) 50 to 90% by mass of a base oil selected fromthe group consisting of a Group II base oil, a Group III base oil, aGroup IV base oil, and any combination thereof; and (B) 10 to 50% bymass of a copolymer of an olefin and an alkyl methacrylate, wherein thecopolymer has a molecular weight of from 1,200 to 50,000.
 16. The methodaccording to claim 15, wherein the gear is in an apparatus forwind-power generation of electricity.
 17. The method according to claim15, wherein the base oil is a polyalphaolefin or a GTL (gas-to-liquid)oil.
 18. The method according to claim 15, wherein the copolymer has aweight average molecular weight of from 7,000 to 20,000.
 19. The methodaccording to claim 15, wherein the lubricating oil composition furthercomprises: (C) 5 to 15% by mass of a carboxylic acid ester compound. 20.The method according to claim 15, wherein the lubricating oilcomposition has a kinematic viscosity at 40° C. of from 140 to 320mm²/s, a viscosity index of not less than 150, and produces no more than1,200 mg/kg of sludge in a Dry TOST test.